It will be easier (in my opinion) getting the conjurer first so that you can do you "Job Quests" as you are leveling and also so you get to learn to play your Job and use your skills in a timely manner. If you plan on doing dungeons as you level up as well you will need some of these abilities to make your life easier.
1. Sword Oath at 30 (Increases the potency of auto-attacks by 50.)
2. Shield Oath at 40 (Reduces damage received by 20%, while lowering damage dealt by 20% and increasing enmity)
Shield Oath really helps you hold "HATE" and keep the mops you are pulling "in line". If you wait to get all these abilities and then start to learn Paladin tanking at 50 you will be behind the curve for sure. As another side note if you wait until 50 you will lose all the XP from those 4 Quests. You will also go 5 levels without the benefit of you AF Gear that you get at level 45 PLD only...cannot get it as Gladiator. Get the Job...plain and simple.